One aspect relates to a device for producing a bone cement paste from a monomer liquid and a cement powder as parent components of the bone cement paste and for delivering the bone cement paste.
One aspect also relates to a method for producing a bone cement paste, for example, a polymethyl methacrylate bone cement paste, using such a device.
One aspect provides, for example, a device for separate storage of the cement powder and of the monomer liquid of polymethyl methacrylate bone cement, for subsequent mixing of the cement powder with the monomer liquid to form a bone cement paste, and for delivery of the bone cement paste, an automatic closure being arranged for opening the device. The device according to one embodiment is in one embodiment a full-prepacked cementing system.
Polymethyl methacrylate (PMMA) bone cements are attributed to the pioneering work carried out by Sir John Charnley (Charnley, J.: Anchorage of the femoral head prosthesis of the shaft of the femur. J. Bone Joint Surg. 42 (1960) 28-30). The monomer component in general contains the monomer methyl methacrylate and an activator dissolved therein (N,N-dimethyl-p-toluidine). The powder component, also known as cement powder or bone cement powder, includes one or more polymers which are produced on the basis of methyl methacrylate and comonomers, such as styrene, methyl acrylate or similar monomers by polymerization, for example, suspension polymerization, an X-ray opaque material and the initiator dibenzoyl peroxide. Mixing of the powder component with the monomer component results, through swelling of the polymers of the powder component in the methyl methacrylate, in a plastically deformable paste, the bone cement or bone cement paste proper. On mixing of the powder component with the monomer component, the activator N,N-dimethyl-p-toluidine reacts with dibenzoyl peroxide to form free radicals. The free radicals formed initiate free-radical polymerization of the methyl methacrylate. As polymerization of the methyl methacrylate proceeds, the viscosity of the bone cement paste increases, until it solidifies.
PMMA bone cements may be mixed in suitable mixing cups using spatulas by mixing the cement powder with the monomer liquid. This may result in air bubbles being entrapped in the bone cement paste, which may have a negative effect on the mechanical properties of the cured bone cement.
To avoid entrapped air in the bone cement paste, a wide range of vacuum cementing systems have been described, of which the following are stated by way of example: U.S. Pat. Nos. 6,033,105 A, 5,624,184 A, 4,671,263 A, 4,973,168 A, 5,100,241 A, WO 99/67015 A1, EP 1 020 167 A2, U.S. Pat. No. 5,586,821 A, EP 1 016 452 A2, DE 36 40 279 A1, WO 94/26403 A1, EP 1 005 901 A2, EP 1 886 647 A1, U.S. Pat. No. 5,344,232 A.
Patents DE 10 2010 019 220 B4, EP 2 596 873 B1 and DE 10 2013 226 118 B3 and patent application DE 10 2014 101 305 A1 disclose devices for mixing PMMA bone cement from two pasty parent components.
A further development in cementing technology is represented by cementing systems in which both the cement powder and the monomer liquid have already been packed in separate compartments of the mixing devices and are mixed together in the cementing system only immediately before application of the cement. Such closed, full-prepacked mixing devices have been proposed in EP 0 692 229 A1, DE 10 2009 031 178 B3, U.S. Pat. Nos. 5,997,544 A, 6,709,149 B1, DE 698 12 726 T2, EP 0 796 653 A2 and U.S. Pat. No. 5,588,745 A.
Patent DE 10 2009 031 178 B3 discloses a storage and mixing device in the form of a full-prepacked cementing system, in which the parent components needed to produce the bone cement paste have already been stored in the storage and mixing device and may be combined and mixed in the storage and mixing device. The storage and mixing device has a two-part delivery plunger for closing a cement cartridge. In this case, a combination of a gas-permeable sterilization plunger and a gas-impermeable sealing plunger is used.
After mixing of the cement powder with the liquid monomer component, polymethyl methacrylate bone cements are applied as bone cement paste in the as yet uncured, pasty state. When using mixing devices, in the case of powder/liquid cements the bone cement paste is located in a cartridge. When applying such conventional PMMA bone cements, after mixing of the two parent components, the bone cement paste formed is expelled using manually operable expulsion devices. The bone cement paste is pushed out of the cartridge through the movement of a delivery plunger. Delivery plungers conventionally have a diameter of between 30 mm and 40 mm and thus a surface area on the outside, against which a rod (frequently also known as a tappet) of the expulsion device acts during the expulsion process, of 7.0 cm2 to 12.5 cm2. Movement of the delivery plunger is for example, brought about by manually operable, mechanical expulsion devices. These manual expulsion devices normally achieve an expulsion force in the range of around 1.5 kN to 3.5 N.
These simple mechanical expulsion devices for example, use clamping rods for expulsion purposes, these being driven by a manually actuatable trigger lever. Manually driven expulsion devices have been tried and tested for decades throughout the world and constitute the existing state of the art. One advantage of these expulsion devices is that, by way of the manual force to be applied, the medical user gains a feel for the bone cement paste's resistance to penetration into the bone structures (cancellous bone).
When using any of the hitherto known full-prepacked cementing systems, the medical user has to perform a plurality of working steps in a predetermined order on the devices in succession until the bone cement paste is obtained and can be applied. Any mistakes in the working steps may lead to failure of the mixing device and therefore cause disruption to the course of the operation. Costly training of medical users is therefore necessary to avoid user error.
WO 00/35506 A1 proposes a device in which polymethyl methacrylate cement powder is stored in a cartridge, wherein the cement powder fills the entire volume of the cartridge and the interspaces between the particles of the cement powder have a volume which corresponds to the volume of monomer liquid necessary to produce bone cement paste with the cement powder stored in the cartridge. This device is constructed such that, through the action of a vacuum, the monomer liquid is introduced from above into the cartridge, wherein to this end a vacuum is applied to a vacuum port at the bottom of the cartridge. In this way, the monomer liquid is drawn through the cement powder, wherein the air located in the interspaces between the cement powder particles is displaced by the monomer liquid. Thorough mechanical mixing with a stirrer of the cement paste formed is thus dispensed with.
One disadvantage of this system is that cement powders which swell rapidly with the monomer liquid cannot be mixed using this device, because the rapidly swelling cement powder particles form a gel-like barrier once the monomer liquid has penetrated by roughly 1 to 2 cm into the cement powder and prevent migration of the monomer liquid throughout the cement powder. Conventional cement powders additionally suffer from the phenomenon that, due to different surface energies, the cement powder particles are only poorly wetted by methyl methacrylate. The methyl methacrylate thereby penetrates only relatively slowly into the cement powder. Furthermore, the risk cannot be ruled out of the monomer liquid being sucked off via the vacuum port under the action of the vacuum once the cement powder has penetrated fully through the monomer liquid. Insufficient monomer liquid is then available for curing by free-radical polymerization or the mixing ratio is modified undesirably and thus also the consistency of the bone cement paste. It is moreover a problem that the air enclosed between the cement powder particles has to be displaced from the top downwards through the monomer liquid, because the air, which is of a lower specific weight than the monomer liquid, has the tendency, due to gravity, to migrate upwards in the cement powder and not to migrate downwards in the direction of the vacuum port.
Electrically driven expulsion devices are also known from the field of adhesives and sealants. These devices may be driven both with primary and secondary cells and also by means of a stationary power supply. With their sometimes very significant expulsion forces, these devices may expel particularly viscous, pasty compositions. One disadvantage of the use of electric motors, however, is that they contain non-ferrous metals and are costly to purchase. In the operating area, which must be kept sterile, such devices have to undergo complex sterilization or even be replaced. Electrical wiring may impede movement of the user while operating.
Pneumatic devices have moreover also been proposed. These apparatuses require a stationary or mobile compressed air connection (U.S. Pat. No. 2,446,501 A, DE 20 2005 010 206 U1). To this end, compressed air hoses are needed, which may impede the user's movement.
It is alternatively also possible to use compressed gas cartridges to provide compressed gas. To this end, devices have been proposed in which the compressed gas inflow is controlled by one valve, with the flow of viscous composition being additionally controlled by a second valve (US 2004/0074927 A1, U.S. Pat. No. 6,935,541 B1). In the case of these devices, the gas cartridges are integrated into the devices. In such systems connected to compressed air or containing compressed gas cartridges, a compressed gas source is always necessary, the systems no longer being usable without such a source.
For these and other reasons, a need exists for the present embodiments.